I am working on a quilt and have decided to use a sashing and an inner boarder. I'm stumped as to the size to cut this sashing and boarder. Is there a ratio to follow? I used a 2-1/2" sashing and boarder for a 12-1/2" block in another quilt I made. Now I'm using a 10-1/2" block and am wondering what size to make this sashing and boarder. Thanks so much!